In general, a reciprocating compressor is designed to form a compression space to/from which an operation gas is sucked/discharged between a piston and a cylinder, and the piston linearly reciprocates inside the cylinder to compress refrigerants.
Most reciprocating compressors today have a component like a crankshaft to convert a rotation force of a drive motor into a linear reciprocating drive force for the piston, but a problem arises in a great mechanical loss by such motion conversion. To solve the problem, development of linear compressors is still under progress.
Linear compressors have a piston that is connected directly to a linearly reciprocating linear motor, so there is no mechanical loss by the motion conversion, thereby not only enhancing compression efficiency but also simplifying the overall structure. Moreover, since their operation is controlled by controlling an input power to a linear motor, they are much less noisy as compared to other compressors, which is why linear compressors are widely used in indoor home appliances such as a refrigerator.
FIG. 1 illustrates one example of a linear compressor in accordance with a prior art.
The conventional linear compressor has an elastically supported structure inside a shell (not shown), the structure including a frame 1, a cylinder 2, a piston 3, a suction valve 4, a discharge valve assembly 5, a linear motor 6, a motor cover 7, a supporter 8, a body cover 9, mainsprings S1 and S2, a muffler assembly 10, and an oil feeder 20.
The cylinder 2 is insertedly fixed to the frame 1, and the discharge assembly 5 constituted by a discharge valve 5a, a discharge cap 5b, and a discharge valve spring 5c is installed to cover one end of the cylinder 2. The piston 3 is inserted into the cylinder 2, and the suction valve 4 which is very thin is installed to open or close a suction port 3a of the piston 2.
The linear motor 6 is installed in a manner that a permanent magnet 6c linearly reciprocates while maintaining the air-gap between an inner stator 6a and an outer stator 6b. To be more specific, the permanent magnet 6c is connected to the piston 3 with a connecting member 6d, and an interactive electromagnetic force between the inner stator 6a, the outer stator 6b, and the permanent magnet 6c makes the permanent magnet 6c linearly reciprocating to actuate the piston 3.
The motor cover 7 supports the outer stator 6b in an axial direction to fix the outer stator 6b and is bolted to the frame 1. The body cover 9 is coupled to the motor cover 7, and between the motor cover 7 and the body cover 9 there is the supporter 8 that is connected to the other end of the piston 3, while being elastically supported in an axial direction by the mainsprings S1 and S2. The muffler assembly 10 for sucking in refrigerant is also fastened to the supporter 8.
Here, the mainsprings S1 and S2 consist of four front springs S1 and four rear springs S2 that are arranged in horizontally and vertically symmetrical positions about the supporter 8. As the linear motor 6 starts running, the front springs S1 and the rear springs S2 move in opposite directions and buff the piston 3 and the supporter 8. In addition to these springs, the refrigerant in the compression space P functions as sort of a gas spring to buff the piston 3 and the supporter 8.
The oil feeder 20 includes an oil feed pipe 21, an oil pump 22, and an oil valve assembly 23, and is configured to communicate with an oil circulation path (not shown) that is formed in the frame 1.
Therefore, when the linear motor 6 starts running, the piston 3 and the muffler assembly 10 connected thereto linearly reciprocate together, and the operation of the suction valve 4 and the discharge valve assembly 5 are controlled automatically with variations in pressure of the compression space P. Through this operation mechanism, refrigerant is sucked into the compression space P after travelling through the suction pipe on the side of the shell, the opening in the back cover 9, the muffler assembly 10, and the suction ports 3a in the piston, is compressed, and then escapes to the outside via the discharge cap 5b, a loop pipe L, and an outflow pipe on the side of the shell.
FIG. 2 illustrates one example of an oil circulation path adapted to a linear compressor in accordance with a prior art. The oil circulation path in a conventional linear compressor is divided into an oil supply path 1in that is formed at a lower, inner portion of the frame 1 and an oil recovery path 1out that is formed at an upper, inner portion of the frame 1. For convenience sake, the oil supply path 1in and the oil recovery path 1out are manufactured in same size and have the same position and the same angle at the upper and lower portions of the frame 1. To be more specific, the oil supply path 1in and the oil recovery path 1out have the same diameter, and an angle A between the oil supply path 1in and the central axis of the cylinder 2 is same as an angle B between the oil recovery path 1out and the central axis of the cylinder 2. Here, the oil supply path 1in is inclinedly positioned to communicate with a portion of the lower side of the frame 1 where the oil valve assembly 23 (see FIG. 1) is mounted and to communicate with the bottom of the cylinder 2. Also, the oil recovery path 1out is inclinedly positioned to communicate with the top of the cylinder 2 and to be exposed to a portion on the top of the frame 1.
When vibrations generated from the linear reciprocating motion of the piston 3 are transmitted to the oil pump 22, a pressure difference is created by the oil pump 22 and by the pressure difference oil at the bottom of the shell is pumped via the oil feed pipe 21 (see FIG. 1). The pumped oil flows along the oil feed pipe 21 (see FIG. 1), the oil valve assembly 23 (see FIG. 1), and the oil supply path 1in, and then is fed between the cylinder 2 and the piston 3 to lubricate/cool them. Thereafter, the oil passes through the oil recovery path 1out and flows down along one side of the frame 1 to be collected at the bottom of the shell.
In the case of the conventional linear compressor, the oil circulation paths of the same size are formed at the top and bottom of the at the same angle, so it is relatively easy to manufacture them. However, as the design degrees of freedom are lowered, the oil feed performance is restricted, and the operation reliability is deteriorated due to imbalances on feed.
Moreover, in the case of the conventional linear compressor, the oil feed pipe and the oil pump are mounted on one side of the frame, while the oil valve assembly that communicates with the oil feed pipe and the oil pump is mounted on the other side of the frame. Thus, even though oil is fed while flowing through the oil feed pipe, the bottom of the oil valve assembly, the oil pump, the top of the oil valve assembly, and the oil supply path, since the path communicating with the oil feed pipe inside the frame, the path communicating with the oil pump, and the oil supply path are formed separately, not only the entire path becomes long, but also the feed performance is impaired by resistance in the path.
As noted earlier, when the linear motor 6 shown in FIG. 1 starts running, the piston 3 and the muffler assembly 10 connected thereto linearly reciprocate together, and the operation of the suction valve 4 and the discharge valve assembly 5 are controlled automatically with variations in pressure of the compression space P encourage the suction valve 4. Through this operation mechanism, refrigerant is sucked into the compression space P after travelling through the suction pipe on the side of the shell, the opening in the body cover 9, the muffler assembly 10, and the suction ports 3a in the piston, is compressed, and then escapes to the outside via the discharge cap 5b, a loop pipe, and an outflow pipe on the side of the shell.
As the piston 3 linearly reciprocates, vibrations are created, and the vibrations cause the oil piston to linearly reciprocate inside the oil pump 22, thereby producing a pressure difference and making oil on the bottom of the shell pump through the oil feed pipe 21. When the oil suction valve and the oil discharge valve are open and closed, the oil passes through the oil valve assemblies 23 and 30 (see FIG. 3) to circulate along the oil circulation path and is recovered back to the bottom of the shell. This circulating oil serves to lubricate/cool the components like the cylinder 2, the piston 3, and so on.
FIG. 3 illustrates one example of an oil valve assembly in a linear compressor in accordance with a prior art. In one example, a conventional oil valve assembly 30 is mounted on one side of a frame (not shown) to communicate with an oil circulation path (not shown) that is formed in the frame, and includes a plate type oil valve 32 in which an oil suction valve 32a and an oil discharge valve 32b for discharging oil are openably/closeably formed, a gasket 34 which is installed to touch a peripheral rim portion of one side of the oil valve 32 that comes in contact with a frame (not shown), so as to prevent an oil leakage, an oil seat 36 which is installed to touch the other side of the oil valve 32 in opposite direction, so as to form a temporary oil storage space, and an oil cover 38.
For the oil valve assembly 30 with the above configuration, the gasket 34, the oil valve 32, the oil seat 36, and the oil cover 38 are laminated in order of mention, and the laminate structure is then screwed to the frame, while the gasket 34 is being adhered closely to the other side of the frame. Of course, the oil suction valve 32a and the oil discharge valve 32b are positioned to communicate with the storage space, and they are either opened or closed depending on an internal pressure of the oil cylinder 32, the storage, and the oil circulation path (not shown), thereby allowing a predetermined amount of oil to flow.
However, in the case of the oil feeder for the conventional linear compressor, the oil feed pipe, the oil pump, and the oil valve assembly, which serve as the oil pumping/circulating mechanism, must be assembled separately or individually. Consequently, there are so many components to work on, and their assembly process is complicate and inconvenient. Furthermore, in some cases oil feed performance is tested after the oil feed pipe, the oil pump, and the oil valve assembly were all assembled to the frame side, but one cannot easily detect, during the production, if there is any defect in the performance of oil feed. This in turn increases defect rate and fails to guarantee good operation reliability.
Besides, in the case of the oil feeder for the conventional linear compressor, the oil valve assembly for opening/closing the oil supply path is made in kit form which includes a gasket, an oil valve, an oil seat, and an oil cover as discussed earlier. However, problems associated with the large number of components to work on and the complicate assembly process still remain unsolved. In addition, bolt joints get weaker after a long period of use, so an oil leakage occurs and operation reliability is degraded.